Identification of the first functional toxin-antitoxin system in Streptomyces.

Toxin-antitoxin (TA) systems are widespread among the plasmids and genomes of bacteria and archaea. This work reports the first description of a functional TA system in Streptomyces that is identical in two species routinely used in the laboratory: Streptomyces lividans and S. coelicolor. The described system belongs to the YefM/YoeB family and has a considerable similarity to Escherichia coli YefM/YoeB (about 53% identity and 73% similarity). Lethal effect of the S. lividans putative toxin (YoeBsl) was observed when expressed alone in E. coli SC36 (MG1655 ΔyefM-yoeB). However, no toxicity was obtained when co-expression of the antitoxin and toxin (YefM/YoeBsl) was carried out. The toxic effect was also observed when the yoeBsl was cloned in multicopy in the wild-type S. lividans or in a single copy in a S. lividans mutant, in which this TA system had been deleted. The S. lividans YefM/YoeBsl complex, purified from E. coli, binds with high affinity to its own promoter region but not to other three random selected promoters from Streptomyces. In vivo experiments demonstrated that the expression of yoeBsl in E. coli blocks translation initiation processing mRNA at three bases downstream of the initiation codon after 2 minutes of induction. These results indicate that the mechanism of action is identical to that of YoeB from E. coli.